Add support for a # prefix in path segments
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To support embedding Handlebars templates in JavaScript classes and
allow them to access private fields, we need property paths segments
to be able to begin with a `#`.
Since `#` is already a control character (i.e. `{{#block}}`), this
parser change implements a new path separator (`.#`), which effectively
creates a new kind of identifier (a path segment identifier) that has
the same lexical structure as any other identifier, but can only appear
at the beginning of a path segment. The `.` and `#` characters count as
a single token, and cannot be separated by whitespace.
This syntax is intended to be used in embedding environments that are
careful about lexical scope, and require an explicit `this.` prefix to
access the current instance.
In classic Handlebars environments, you would expect `{{this.#foo}}` to
be equivalent to `{{#foo}}`, but that would parse as a block start,
which would be ambiguous.
In the future, it would be helpful to explicitly document the strict
lexical subset of Handlebars, but this change doesn't *break* classic
Handlebars. In classic Handlebars contexts, this change would make
`this.#foo` work without needing `this[#foo]`. It might seem surprising
that `#foo` isn't equivalent to `this.#foo`, but it's not a breaking
change and the reason that `{{#foo}}` can't parse as a path is fairly
obvious.
|
I think you have to either add the changes in |
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To support embedding Handlebars templates in JavaScript classes and allow them to access private fields, we need property paths segments to be able to begin with a
#.Since
#is already a control character (i.e.{{#block}}), this parser change implements a new path separator (.#), which effectively creates a new kind of identifier (a path segment identifier) that has the same lexical structure as any other identifier, but can only appear at the beginning of a path segment. The.and#characters count as a single token, and cannot be separated by whitespace.This syntax is intended to be used in embedding environments that are careful about lexical scope, and require an explicit
this.prefix to access the current instance.In classic Handlebars environments, you would expect
{{this.#foo}}to be equivalent to{{#foo}}, but that would parse as a block start, which would be ambiguous.In the future, it would be helpful to explicitly document the strict lexical subset of Handlebars, but this change doesn't break classic Handlebars. In classic Handlebars contexts, this change would make
this.#foowork without needingthis.[#foo]. It might seem surprising that#fooisn't equivalent tothis.#foo, but it's not a breaking change and the reason that{{#foo}}can't parse as a path is fairly obvious.